2WD (Two-Wheel Drive) FAQ

[Hangdog98]

So I've been following this with keen interest and I started to do so because I wanted to experiment with dual Q100's on a road bike running a single battery. When I began this journey into 2WD I was hypothesising that two motors would provide double the available torque of one motor OR for my application, the same torque at half the Amps on a given hill, with half the heat, give or take. This is my reason for considering two motors though I'm still not sure if this is correct. Can anyone provide this answer

If you feel compelled to tell me that I only need one motor twice the size, please try and resist the urge, I get that. I want very small lightweight under-stressed geared hub motors for this build.

Regarding the throttle(s), I planned a mechanical solution instead of an electrical one by grafting the two throttle mechanisms together on the one twist grip, keeping their wiring intact and running them to their respective controllers. Has anyone tried that solution?

[motomech]

So I've been following this with keen interest and I started to do so because I wanted to experiment with dual Q100's on a road bike running a single battery. When I began this journey into 2WD I was hypothesising that two motors would provide double the available torque of one motor OR for my application, the same torque at half the Amps on a given hill, with half the heat, give or take. This is my reason for considering two motors though I'm still not sure if this is correct. Can anyone provide this answer

If you feel compelled to tell me that I only need one motor twice the size, please try and resist the urge, I get that. I want very small lightweight under-stressed geared hub motors for this build.

Regarding the throttle(s), I planned a mechanical solution instead of an electrical one by grafting the two throttle mechanisms together on the one twist grip, keeping their wiring intact and running them to their respective controllers. Has anyone tried that solution?

I only played Devil's Advocate with the previous poster to Point out that to climb one moderate hill, 2WD really isn't needed

I just ordered a q100 rear to match up with my MXUS frt. I had been holding off, trying to figure out which wind to go with. Not easy given BMS Battery's obtuse labeling system , but recently, both Grindz and Zukster have confirmed that the that the BMS Battery's 201 "slow-wind" is not really a slow-wind. More like a mid-speed, probably close to the MXUS's 255 rpm @ 36V[maybe BMS B. used a speed measured @ 24V

At any rate, there are good reasons to go with 2WD, IMO.
In my case there are three,
1]I already have a MXUS on the frt. and I like it a lot. And it doesn't stress the forks and I can be secure with one off-the-shelf torque arm..
2]I'm retiring this year and moving back to Tucson Az. and I want to do some "light' trail riding and I think 2WD would be fun for that/
3]I like to tinker and "fustz" w/wiring and things electrical..
The obvious question is, " Why not go with another MXUS, indeed, why not?". It could well be the best of the mini.s and the price is right. And there are reasons the go with an exact match[battery, controller and motor]as Miuan has pointed out. But I think the Q100 is close enough and it has some advantages when used as a rear mount, namely will fit a 9-speed freewheel and the wires exit on the left[non drive-line]side.
Researching here, I've come to the conclusion that 2WD systems come in two flavors, each with a different set of "do's and don't".
What we are talking about, dual mini's is one, the other being dual powerful motors and motors of mixed types[geared and DD's].
If we stick with the first, dual mini's, things become much easier I.M.O.

QUOTE "When I began this journey into 2WD I was hypothesising that two motors would provide double the available torque of one motor OR for my application, the same torque at half the Amps on a given hill, with half the heat, give or take. "

Yup, The biggy being the heating up part. As Dogman has pointed out on various occassions, heat saturation on hills is the Achilles Heal of the Mini Motor. On steep, long hills, the speed drops into the lee-side of the efficiency curve, more heat than motive force is generated, and the " vicious cycle" begins[vicious as in a Chihuahua can be vicious].

EDIT Opps, i hit submit by mistake. Oh well, it's Sat nite, the girls have passed out and I'm a bit drunk....
To be continued...

P.S. You might want to check out Garykards thread, Dual Cute Motors, I think it was titled.

[Kingfish]

Generally you will consume more power than one motor doing all the work, and less than two motors sharing the load. The best use of 2WD is starting off the line and hill-climbing. The least benefit is when cruising on level ground; often one motor just tags along and lets the other take the load – or they go into contention if the two wheels and controllers are set identical. To prevent contention on my ebike, I deliberately set each wheel to a different physical size, and overtly set the power-levels different as well which worked out pretty dang well.

If you are looking to gain efficiency – this is not the thread for you. The fact is that 2WD can and does provide about twice the torque to the ground over a single motor at the same power; two motors individually set to X-wattage will push roughly twice as fast as a single motor set to X-wattage. Another way to look at it: 2WD will get off the line and climb hills faster and cooler than a single-wheel at twice the power; two motors using a total of X-wattage will outperform (though at an economic price) a single motor at the same X-wattage. The downside to 2WD is that you have twice the weight and twice the freewheel drag, but then you get twice the regen braking.

There is no free lunch: 2WD will use more power than a single-wheel drive.
It’s also a heck of a lot of fun! KF

[motomech]

Generally you will consume more power than one motor doing all the work, and less than two motors sharing the load. The best use of 2WD is starting off the line and hill-climbing. The least benefit is when cruising on level ground; often one motor just tags along and lets the other take the load – or they go into contention if the two wheels and controllers are set identical. To prevent contention on my ebike, I deliberately set each wheel to a different physical size, and overtly set the power-levels different as well which worked out pretty dang well.

If you are looking to gain efficiency – this is not the thread for you. The fact is that 2WD can and does provide about twice the torque to the ground over a single motor at the same power; two motors individually set to X-wattage will push roughly twice as fast as a single motor set to X-wattage. Another way to look at it: 2WD will get off the line and climb hills faster and cooler than a single-wheel at twice the power; two motors using a total of X-wattage will outperform (though at an economic price) a single motor at the same X-wattage. The downside to 2WD is that you have twice the weight and twice the freewheel drag, but then you get twice the regen braking.

There is no free lunch: 2WD will use more power than a single-wheel drive.
It’s also a heck of a lot of fun! KF

I'm not particualy interested in overall power consumption, not going to be hyper-mile'ing and if I need more range, I'll add more Lipo. My reference to efficiency was in regards to being able to climb a formidable hill @ more than 5-8 mph and not self-destruct a single mini motor. Yes, there have been claims of increased efficiency running two SMALL motors[one rider claiming incredible gains], but until I can explore that myself I tend to dismiss them. It seems clear from real-world 2WD users[of which you are the King], that there will be a loss in efficiency.
But almost all of these discussions[including yours]are from the POV of using two POWERFULL motors.
Real world reports of two small motor set-ups are more rare, Garykard and Chinaphil come to mind. There is evidence that running two small motors all the time may not extract a major penality[as a side note, it would seem that both Chinaphil and Garykard have moved on to Mac rear drives. This should probably tell me something ].
Aside from the LARGE and SMALL motor 2WD catogories, there can be futher sub-divisions as described by John in CR,

"For the mountains and going slow I'd use identical lower speed wind motors that they call the torque model.....The reason I'd say identical motors is the high stress of steep climbs. You want to share that load equally. For street riding a difference in torque for the two motors could make sense, and that's the route I'm considering with less torque but higher speed capability of the front motor. My goal is different though, and I'm after maximum acceleration and speed while not so much on the front that the wheel spins. That route I get a large wheel on front, which I prefer at the speeds I ride, and the front motor will always be assisting the rear. I will have to dial in the current settings, so the front doesn't get stressed and overheat from carrying too much of the load.".

So what we have here is one approach where the two motors/controllers are the same[in this discussion, I am assuming one battery, as there would appear to be no benefit to using two]and the goal is to raise the performance levels within the parameters of the single motor envelope. The exception here, and this might be considered in the realm of increased efficiency, would be the ability of two small motors to help "pull" each other slightly higher into the zone between power/load and no-load speed. Reports of two small motors vs. one seem to bear this out. For a mini motor user, increasing top speed from say, 21-23 mph to 23-24 mph without raising the voltage is deffinately a big deal.

The second approach attempts to expand the parameters by over-lapping winds, types, controllers, etc.

Since I am seeking a light duty trail bike[more like trials actually] and have no desire to be able to exceed 23-24 mph[Tucson has a wonderful network of bike trails/lanes, but it also has an enforced bicycle speed limit of 20 mph], I am interested in the first approach. And it just seems more elegant to me.
Muian said'

"To run 2 motors, you need two controllers, one throttle and one battery. It's best to combine 2 identical controllers to make sure both will have the same understanding of throttle signal. The same applies to motors, but sometimes a motor you like is not available for front and rear, so then you have to match 2 motors that will have same or very similar no load speed, and play with the simulator to make sure the motors will pull together well."

He, as well as others[Neptronix in particular]go on to say[and I am paraphasing], for a street machine, up to speeds that a mid-sized gear motor can achieve on moderate voltage, one is better off just using a rear Mac/Puma/BMC or BPM. Very effective, less complicated and in the case of the BPM, less expensive. Heck, for the serious off-roader this probably would be a better approach, as it would keep the frt. end light, enabling the rider to loft over trail obstacles. I rode dirt bikes for over 40 years and I understand this well, but I am at the point in life where I would be more inclined to stop, get off, and carry the bike over something like a log.

So now we come full circle and get back to the questions of how to do a 2WD mini-motor rig.
As I mentioned in an earlier post, I think one of the advantages to using low-powered motors is the freedom from worry about applying frt. to rear power differential. Sure, I can get my frt. mounted MXUS to spin on dry pavement, but I have to try and do so. And a spinning frt. tire is easier to control than a rear.
For a purely street ride, I would be inclined to simply run both controllers off one throttle[no mechanical hash-ups are needed]with one switch to drop one motor out of the loop if so desired. Or better yet, one throttle into a Cycle Analyst as Justin has described and one of the two out switched. Which motor to run at say, 80% cruise? Not sure, since I will be using two slightly different motors some experimentation would be required[the fun begins].
For off-road, i think two throttles would provide max. giggles. I already use a trigger left-mounted so it is a "pusher', so it seems to me that adding a right-hand half twist would be the most intuitive set-up. They both require a "forward" motion.
Combining these two approaches would obviously require some creative switching networks, even more fun

[Alan B]

Two motors provide the torque of one at essentially the same total current, but in the dual motor case the per motor current is half.

Most people experienced in this indicate that a spinning front tire is harder to control than a spinning rear tire. The front tire is used for balance control, when it is out of traction balance is quickly lost. Whereas a spinning rear tire can be compensated for by steering the bike under the center of gravity maintaining system balance.

On the efficiency issue, for motors operated in their good efficiency region, two are just slightly less efficient than a single; but for the situation where a single motor is operated in a region of low efficiency or overheat dropping the power in half and adding a second motor can raise the efficiency and lower the heating in each motor and produce a net efficiency gain. This typically would be in the very low speed high torque region.

Two small motors will be really stealth if the rest of the gear and wiring can be hidden. Having two separate controllers also will provide a ride home capability in the case of a controller, hall or motor failure.

Combining two throttles into one needs to be done carefully to avoid the magnets interfering with each other. Some have used a single magnet but dual hall sensors to accomplish this.

[Kingfish]

Good stuff guys.

• +2 Both motors equal. The field tests agree
• +2 Both controllers equal. Likewise with above I agree completely, although with different power settings to avoid contention. The alternative is a <hint hint> multichannel (initially-dual) controller that understands and compensates when one wheel slips more than the other. Downgrading the front will prevent slippage; the amount though depends upon the terrain and environment and tires. If it were an easy option, I would like to change the ratio of sharing on-the-fly so long as contention was managed. See next item.
• +1 on the Unified Throttle; work needs to be done here to create a commercial offering. As a wishful feature, imagine a secondary ring that could be set on-the-fly that balances attenuates the signal of A||B from 1:1 to < 1. The idea came to me from an old A/V receiver that had two volume controls: Gross & Fine on concentric rings. The load-sharing ring would simply attenuate the selected (or perhaps non-favored) signal. This in my mind would provide quite a bit of control, and complement the 3-Way current control. Ah, here's a thought: The Throttle and 3-Way should be unified as well – right where the thumb can get to it.

Hmmm <rub chin>, now if only we had cruise control with persistent presets…
<slurp coffee> KF

[hjns]

Hi all,

Just reporting back about my experiences.


I have tried 2WD with front 9C 2810 and rear HT 3525 on 20S3P for a couple of weeks. Initially, I had the 9C axle rotating out of the front dropouts, destroying the dropouts of my Fox TALAS fork. Cause was identified as too much torque and not enough torque arm (only one). After fixating with 2 torque arms, no issues there anymore. I used the unified throttle with dual Hall sensors to 2 Lyen sensorred 12 FET controllers, fed by a single 20S3P pack. The throttle would give first a signal to the rear and at a speed of about 5km/h would also start driving the front motor. Total bike weight was about 30kg including two motors, 2 controllers, 10kg lipo pack.

In short; I did not like it.

Advantages
Hill climbing was super. Just great, and with 10% hills, I felt I could climb forever. None of the motors would even get warm. I could climb them with speeds over 45 km/h, and not even going WOT. Never tried WOT, because all hill-roads here are snaking around the hills, so 45 km/h is already quite fast.

Pulling the trailer with the kids was also super. And biking with a lot of wind was - due to the large weight - also super, with great tracking.

Disadvantages
However, for commuting and drafting through traffic, such a heavy bike is just not fun. It might as well be a scooter. The real advantage of an E-bike for me is it's capability to go where scooters and motors can not go or are not allowed to go. And these are precisely the parts of the road where a lighter bike makes a difference. Therefore, I removed the front 9C motor and the second controller, and continued biking with "just" the rear HT 3525. Initially on 20S, now also on 30S, reaching speeds >70km/h (42mph). On my 2WD, I would feel very insecure at those speeds. 50km/h was really the max. Now, with the lighter bike, 75km/h is a nice challenge, but does not feel unsafe.

Another disadvantage I noticed was the difference in front wheel and the effect on front suspension. With each bump, the front suspension had noticable difficulties dealing with it. No change in front suspension configuration (increase/decrease air pressure, rebound, more/less sag, etc) could get rid of that. Also, the added mass in the front wheel made it much more difficult to deal with more technical parts of an off-road bike trail. I do not have a lot of experience with that, but without the front motor I can much better deal with off-road trails.

Conclusion
So, I reverted back to RWD, and I will probably stick with this configuration. 2WD was a good experience and learning curve for me. Time to move on.

[wojtek]

many thanks for sharing your experience Henk, very interesting!

[hodgie]

@hjns: Yes, thanks, that was alot of explanation, but very valuable to me.

[Lebowski]

So Henk, you got a front wheel for sale now ?

[hjns]

Hi all,

I am happy to see that some people find my experience useful.

No, the front 9C 2810 is not for sale. Within two months we will be moving to a house in a much more hilly area (Dornach-Gempen). Therefore, I will probably try 2WD again as a "plugin". That will then really be a balance between going uphill with superspeed versus going downhill with the added weight of the second motor. I have a feeling I know the answer, but I just don't want to give up on 2WD completely...

[hjns]

I think it is important to emphasize in this FAQ that there is probably a huge difference between a high power 2WD setup and a low power 2WD setup. My high power 2WD setup was based around a rear HT3525 at 20S (74V) and with a front motor added to it. This setup was meant for high speed (40mph) commuting, with the occasional 10% hill, and the even less often off-road experience. The HT3525 is about 8kg, and the 9C 2810 slightly less. Therefore, having both motors made for superfast hill climbing and less for off road.

Now, I can imagine that a low power 2WD will handle completely different, especially with the V3 CA and a nice torque sensor as described here. If one would have a 3kg motor in front and a 3kg motor in the rear, together with a 5-6kg lipo pack, I think the weight would be very much less a factor. Of course, 3kg extra in the front is still significant, but here the disadvantages of the suffering handling would maybe offset by the advantages of the 2WD hill climbing.

[Alan B]

DIfferential Buffer for Throttle

The large currents flowing through the resistance of the ground cables between the controllers causes their throttle signals to vary. Using a differential buffer amplifier will re-reference the voltage to the controllers ground even when the grounds are varying with respect to each other. I suspect this is causing Kingfish's occasional "shutdown" of his slave controller as it sees throttle input voltages exceeding the allowed max value in some circumstances.



Note that there are many differential amplifier chips out there and not all are suitable for this application. This unit needs to run on 0 and 5 volts and be able to handle a differential input signal below its own "ground". Most of these parts are surface mount but there are a few through-hole parts. Surface mount may be necessary to get the required features.

You can construct a differential amplifier with an operational amplifier and precision resistors, but the precision required for good performance is difficult to attain. Differential amplifier chips are laser trimmed so the resistors match accurately.

[Kingfish]

Thank you Alan B. I would not have understood this issue a week ago, and it is only because of the very recent work we've been doing on Solving the Variable Ebrake-Throttle Problem that I am able to comprehend the value of Op and Differential Amps.

Very appreciative and well-said, KF

[knighty]

had a look but couldn't see this being asked before

why not just run a more powerful controller, and then power both wheels in parallel ?
(no sensors, or only one wheel with hall sensors)

I've been thinking more and more about 2wd... and this would make it nice and easy... no throttle problem or wheels trying to go different speeds etc.. ?


for me, I think I'd run the rear wheel as it is now, with it's hall sensors, and then just parallel the front wheel in with the 3 phases going to the rear wheel

and jump from a 2kw controller to a 4kw controller
(or even more powerful)

[Alan B]

...

why not just run a more powerful controller, and then power both wheels in parallel ?
(no sensors, or only one wheel with hall sensors)

I've been thinking more and more about 2wd... and this would make it nice and easy... no throttle problem or wheels trying to go different speeds etc.. ?

...

This only works if the two BLDC motors are mechanically phased the same at all times (or are brushed type motors).

[Hangdog98]

I want to make a dual Q100 road bike but the shipping costs from BMS Battery have gone waaaaay up. I'm in Sydney Australia which is relatively close to China and they want $500+ just for shipping to send two wheel kits @ $126 a piece. The total was nearly eight hundred and fifty bucks! I tried to buy a $5 throttle and the shipping was $95!

Seriously, for $850 I could fly to China, spend two nights in a hotel, go to a trade expo and fly home with the Q100's in my hand luggage. (If I had the time) .

So my question is; Are there any other suppliers of the Q100 motors that have more reasonable shipping prices?

[renaud]

Try green bike kit : 420$ for 2 Q100, one front and one rear @115$ each.

http://www.greenbikekit.com/

[amberwolf]

Those may be the same company:
viewtopic.php?f=3&t=44684
as well as ecitypower.

Or they might simply be run by ex-employees of BB/EP

[CORBINFIBER]

This bike is about to be three wheel drive with pusher a trailer ,,, three hubs in three 29ers with three disk and regen brakes


I want 50mph up hill
Stage three includes
upgrading all wires
Ceramic bearings
Hempfiber aero kit

[docnjoj]

That is some great riding Corbinfiber but you have to admit those are pretty short hills. What happens on a mile or 2 of 10%? Looks like "melt city" for the motors.
otherDoc

[CORBINFIBER]

I live in hollywood los Angeles and you know the mountain with the hollywood sign? I traverse it 15 miles at WOT 35-40 mph and the motors and controllers barely warm up,, my third motor i hope will get me closer to 50mph up it,,, and the third Disc brake will be nice going down it